Coal compositions for catalytic gasification

ABSTRACT

Particulate compositions are described comprising an intimate mixture of a coal and a gasification catalyst in the presence of steam to yield a plurality of gases including methane and at least one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons are formed. Processes are also provided for the preparation of the particulate compositions and converting the particulate composition into a plurality of gaseous products.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application Ser. No. 61/032,685 (filed Feb. 29, 2008), thedisclosure of which is incorporated by reference herein for all purposesas if fully set forth.

FIELD OF THE INVENTION

The invention relates to particulate compositions of coal and at leastone alkali metal gasification catalyst, one transition metalgasification catalyst, and one alkaline earth metal source. Further, theinvention relates to processes for preparation of the particulatecompositions and for gasification of the same in the presence of steamto form gaseous products, and in particular, methane.

BACKGROUND OF THE INVENTION

In view of numerous factors such as higher energy prices andenvironmental concerns, the production of value-added gaseous productsfrom lower-fuel-value carbonaceous feedstocks, such as biomass, coal andpetroleum coke, is receiving renewed attention. The catalyticgasification of such materials to produce methane and other value-addedgases is disclosed, for example, in U.S. Pat. No. 3,828,474, U.S. Pat.No. 3,998,607, U.S. Pat. No. 4,057,512, U.S. Pat. No. 4,092,125, U.S.Pat. No. 4,094,650, U.S. Pat. No. 4,204,843, U.S. Pat. No. 4,468,231,U.S. Pat. No. 4,500,323, U.S. Pat. No. 4,541,841, U.S. Pat. No.4,551,155, U.S. Pat. No. 4,558,027, U.S. Pat. No. 4,606,105, U.S. Pat.No. 4,617,027, U.S. Pat. No. 4,609,456, U.S. Pat. No. 5,017,282, U.S.Pat. No. 5,055,181, U.S. Pat. No. 6,187,465, U.S. Pat. No. 6,790,430,U.S. Pat. No. 6,894,183, U.S. Pat. No. 6,955,695, US2003/0167961A1,US2006/0265953A1, US2007/000177A1, US2007/083072A1, US2007/0277437A1 andGB 1599932.

To improve the gasification of coal, techniques have been suggested foradmixing coal with a selected catalyst, or catalysts. Known methodsinclude (a) physically admixing of catalyst with the coal, and (b)incipient wetness impregnation, where a catalyst-containing solution isadded to a dry coal, and the volume of the solution is not in excess,but is instead just enough to completely fill the pores of the coal.These methods of coal impregnation suffer the drawback of producing acoal with catalyst loading that is not highly dispersed, and thus a coalwith reduced gasification efficiency. The art has placed little emphasison catalyst-loaded coal with highly dispersed catalyst loading, andprocesses to prepare same. Accordingly, a need exists in the art forproviding new catalyst compositions to increase the yield of combustiblegaseous products from catalytic coal gasification. At the same time,there is a need for improved methods of catalyst loading that can alsobe carried out in a manner that permits efficient recycling of thesolutions used to load catalyst onto coal, thereby reducing rawmaterials costs and minimizing the generation of waste products from thecatalyst loading process.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a particulate compositioncomprising an intimate mixture, the intimate mixture comprising (a) acoal particulate loaded with a transition metal gasification catalyst;(b) a coal particulate loaded with an alkaline earth metal source; and(c) a coal particulate loaded with an alkali metal gasificationcatalyst; wherein: (i) the coal particulates have a size distributionsuitable for gasification in a fluidized bed zone; (ii) in the presenceof steam and under suitable temperature and pressure, the gasificationcatalysts exhibit gasification activity whereby a plurality of gases,including methane and at least one or more of hydrogen, carbon monoxide,carbon dioxide, hydrogen sulfide, ammonia, and other higher hydrocarbonsare formed; (iii) the transition metal gasification catalyst is presentin an amount sufficient to provide, in the particulate composition, aratio of transition metal atoms to carbon atoms ranging from about 0.001to about 0.10; (iv) the alkaline earth metal source is present in anamount sufficient to provide, in the particulate composition, from about0.1 wt % to about 3.0 wt % of alkaline earth metal atoms on a dry basis;and (v) the alkali metal gasification catalyst is present in an amountsufficient to provide, in the particulate composition, a ratio of alkalimetal atoms to carbon atoms ranging from about 0.01 to about 0.08.

In a second aspect, the invention provides a process for converting aparticulate composition into a plurality of gaseous products, theprocess comprising the steps of: (a) supplying a particulate compositionaccording to the first aspect of the invention to a gasificationreactor; (b) reacting the particulate composition in the gasificationreactor in the presence of steam and under suitable temperature andpressure to form a plurality of gaseous products, including methane andat least one or more of hydrogen, carbon monoxide, carbon dioxide,hydrogen sulfide, ammonia, and other higher hydrocarbons; and (c) atleast partially separating the plurality of gases to produce a streamcomprising a predominant amount of one or more of the gaseous products.

In a third aspect, the invention provides a process for preparing aparticulate composition, the process comprising the steps of: (a)providing a first coal feedstock, a second coal feedstock, and a thirdcoal feedstock, each in particulate form; (b) contacting the first coalfeedstock with a first aqueous solution comprising a transition metalgasification catalyst to form a first slurry; (c) contacting the secondcoal feedstock with a second aqueous solution comprising an alkalineearth metal source to form a second slurry; (d) contacting the thirdcoal feedstock with a third aqueous solution comprising an alkali metalgasification catalyst to form a third slurry; (e) dewatering the firstslurry, the second slurry, and the third slurry to form a first wetcake, a second wet cake, and a third wet cake, respectively; (f)thermally treating the first wet cake, the second wet cake, and thethird wet cake with a dry inert gas to provide a first particulate, asecond particulate, and a third particulate, each having a residualmoisture content of less than about 4 wt %; and (g) blending at least aportion of the first particulate, at least a portion of the secondparticulate, and at least a portion of the third particulate to form aparticulate composition.

In a fourth aspect, the invention provides a process for preparing aparticulate composition, the process comprising the steps of: (a)providing a first coal feedstock, a second coal feedstock, and a thirdcoal feedstock, each in particulate form; (b) contacting the first coalfeedstock with a first aqueous solution comprising a transition metalgasification catalyst to form a first slurry; (c) contacting the secondcoal feedstock with a second aqueous solution comprising an alkalineearth metal source to form a second slurry; (d) contacting the thirdcoal feedstock with a third aqueous solution comprising an alkali metalgasification catalyst to form a third slurry; (e) dewatering the firstslurry, the second slurry, and the third slurry to form a first wetcake, a second wet cake, and a third wet cake, respectively; (f)combining at least a portion of the first wet cake, at least a portionof the second wet cake, and at least a portion of the third wet cake toform a final wet cake; and (g) thermally treating the final wet cakewith a dry inert gas to provide a particulate composition having aresidual moisture content of less than about 4 wt %.

In a fifth aspect, the invention provides a particulate compositionprepared according to the third aspect of the invention or the fourthaspect of the invention.

DETAILED DESCRIPTION

The present invention relates to particulate compositions, methods forthe preparation of the particulate compositions, and methods for thecatalytic gasification of particulate compositions. The methods of thepresent invention provide novel coal particulate compositions whichcomprise finely dispersed transition metal gasification catalyst, alkalimetal gasification catalyst, and an alkaline earth metal source. Theprocesses allow for the generation of such dispersed transition metals,alkali metals, and alkaline earth metals within the pores of the coalparticulate, thereby enabling greater catalyst gasification activity andincreased production of desired product gases (e.g., methane).Generally, the particulate composition includes various blends of, forexample, high-ash- and/or high-moisture-content coals, particularlylow-ranking coals such as lignites, sub-bituminous coals, and mixturesthereof. Such particulate compositions can provide for an economical andcommercially practical process for catalytic gasification of coals, suchas lignites or sub-bituminous coal, with high ash and moisture contentsto yield methane and other value-added gases as a product.

The present invention can be practiced, for example, using any of thedevelopments to catalytic gasification technology disclosed in commonlyowned US2007/0000177A1, US2007/0083072A1 and US2007/0277437A1; and U.S.patent application Ser. No. 12/178,380 (filed 23 Jul. 2008), U.S. Ser.No. 12/234,012 (filed 19 Sep. 2008) and U.S. Ser. No. 12/234,018 (filed19 Sep. 2008). All of the above are incorporated by reference herein forall purposes as if fully set forth.

Moreover, the present invention can be practiced in conjunction with thesubject matter of the following U.S. Patent Applications, each of whichwas filed on Dec. 28, 2008: U.S. Ser. No. 12/342,554, entitled“CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROMCHAR”; U.S. Ser. No. 12/342,565, entitled “PETROLEUM COKE COMPOSITIONSFOR CATALYTIC GASIFICATION”; U.S. Ser. No. 12/342,578, entitled “COALCOMPOSITIONS FOR CATALYTIC GASIFICATION”; U.S. Ser. No. 12/342,596,entitled “PROCESSES FOR MAKING SYNTHESIS GAS AND SYNGAS-DERIVEDPRODUCTS”; U.S. Ser. No. 12/342,608, entitled “PETROLEUM COKECOMPOSITIONS FOR CATALYTIC GASIFICATION”; U.S. Ser. No. 12/342,628,entitled “PROCESSES FOR MAKING SYNGAS-DERIVED PRODUCTS”; U.S. Ser. No.12/342,663, entitled “CARBONACEOUS FUELS AND PROCESSES FOR MAKING ANDUSING THEM”; U.S. Ser. No. 12/342,715, entitled “CATALYTIC GASIFICATIONPROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR”; U.S. Ser. No.12/342,736, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OFALKALI METAL FROM CHAR”; U.S. Ser. No. 12/343,143, entitled “CATALYTICGASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR”; U.S. Ser.No. 12/343,149, entitled “STEAM GENERATING SLURRY GASIFIER FOR THECATALYTIC GASIFICATION OF A CARBONACEOUS FEEDSTOCK”; and U.S. Ser. No.12/343,159, entitled “CONTINUOUS PROCESSES FOR CONVERTING CARBONACEOUSFEEDSTOCK INTO GASEOUS PRODUCTS”. All of the above are incorporated byreference herein for all purposes as if fully set forth.

Further, the present invention can be practiced in conjunction with thesubject matter of the following U.S. Patent Applications, each of whichwas filed concurrently herewith: Ser. No. 12/395,293, entitled“PROCESSES FOR MAKING ABSORBENTS AND PROCESSES FOR REMOVING CONTAMINANTSFROM FLUIDS USING THEM”; Ser. No. 12/395,309, entitled “STEAM GENERATIONPROCESSES UTILIZING BIOMASS FEEDSTOCKS”; Ser. No. 12/395,320, entitled“REDUCED CARBON FOOTPRINT STEAM GENERATION PROCESSES”; Ser. No.12/395,330, entitled “PROCESS AND APPARATUS FOR THE SEPARATION OFMETHANE FROM A GAS STREAM”; Ser. No. 12/395,344, entitled “SELECTIVEREMOVAL AND RECOVERY OF ACID GASES FROM GASIFICATION PRODUCTS”; Ser. No.12/395,353, entitled “COAL COMPOSITIONS FOR CATALYTIC GASIFICATION”;Ser. No. 12/395,372, entitled “CO-FEED OF BIOMASS AS SOURCE OF MAKEUPCATALYSTS FOR CATALYTIC COAL GASIFICATION”; Ser. No. 12/395,381,entitled “COMPACTOR-FEEDER”; Ser. No. 12/395,385, entitled “CARBONACEOUSFINES RECYCLE”; Ser. No. 12/395,429, entitled “BIOMASS CHAR COMPOSITIONSFOR CATALYTIC GASIFICATION”; Ser. No. 12/395,433, entitled “CATALYTICGASIFICATION PARTICULATE COMPOSITIONS”; and Ser. No. 12/395,447,entitled “BIOMASS COMPOSITIONS FOR CATALYTIC GASIFICATION”. All of theabove are incorporated herein by reference for all purposes as if fullyset forth.

All publications, patent applications, patents and other referencesmentioned herein, if not otherwise indicated, are explicitlyincorporated by reference herein in their entirety for all purposes asif fully set forth.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. In case of conflict, thepresent specification, including definitions, will control.

Except where expressly noted, trademarks are shown in upper case.

Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present invention,suitable methods and materials are described herein.

Unless stated otherwise, all percentages, parts, ratios, etc., are byweight.

When an amount, concentration, or other value or parameter is given as arange, or a list of upper and lower values, this is to be understood asspecifically disclosing all ranges formed from any pair of any upper andlower range limits, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the present invention be limited to thespecific values recited when defining a range.

When the term “about” is used in describing a value or an end-point of arange, the invention should be understood to include the specific valueor end-point referred to.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but can include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

The use of “a” or “an” to describe the various elements and componentsherein is merely for convenience and to give a general sense of theinvention. This description should be read to include one or at leastone and the singular also includes the plural unless it is obvious thatit is meant otherwise.

The materials, methods, and examples herein are illustrative only and,except as specifically stated, are not intended to be limiting.

Coal

The term “coal” as used herein means peat, lignite, sub-bituminous coal,bituminous coal, anthracite, or mixtures thereof. In certainembodiments, the coal has a carbon content of less than about 90%, lessthan about 85%, or less than about 80%, or less than about 75%, or lessthan about 70%, or less than about 65%, or less than about 60%, or lessthan about 55%, or less than about 50% by weight, based on the totalcoal weight. In other embodiments, the coal has a carbon content rangingup to about 90%, or up to about 85%, or up to about 80%, or up to about75% by weight, based on the total coal weight. Examples of useful coalsinclude, but are not limited to, Illinois #6, Pittsburgh #8, Beulah(ND), Utah Blind Canyon, and Powder River Basin (PRB) coals. Anthracite,bituminous coal, sub-bituminous coal, and lignite coal may contain about10 wt %, from about 5 to about 7 wt %, from about 4 to about 8 wt %, andfrom about 9 to about 11 wt %, ash by total weight of the coal on a drybasis, respectively. However, the ash content of any particular coalsource will depend on the rank and source of the coal, as is familiar tothose skilled in the art. See, e.g., Coal Data: A Reference, EnergyInformation Administration, Office of Coal, Nuclear, Electric andAlternate Fuels, U.S. Department of Energy, DOE/EIA-0064(93), February1995.

Catalyst Components

Particulate compositions according to the present invention are based onthe above-described coal and further comprise an amount of an alkalimetal gasification catalyst, a transition metal gasification catalyst,and an alkaline earth metal source.

The alkali metal gasification catalyst can be an alkali metal and/or acompound containing alkali metal atoms. For example, the alkali metalgasification catalyst can comprise one or more alkali metal complexes(e.g., coordination complexes formed with one or more reactivefunctionalities on the surface or within the pores of the coalparticulate, such as carboxylic acids and/or phenolic groups) formedwith the coal particulate.

Typically, the quantity of the alkali metal component in the compositionis sufficient to provide, in the particulate composition, a ratio ofalkali metal atoms to carbon atoms ranging from about 0.01, or fromabout 0.02, or from about 0.03, or from about 0.04, to about 0.06, or toabout 0.07, or to about 0.08.

Suitable alkali metals include lithium, sodium, potassium, rubidium,cesium, and mixtures thereof. Particularly useful are potassium sources.Suitable alkali metal sources include alkali metal carbonates,bicarbonates, formates, oxalates, amides, hydroxides, acetates, orsimilar compounds. For example, the catalyst can comprise one or more ofsodium carbonate, potassium carbonate, rubidium carbonate, lithiumcarbonate, cesium carbonate, sodium hydroxide, potassium hydroxide,rubidium hydroxide or cesium hydroxide, and particularly, one or morepotassium complexes formed with the coal particulate, potassiumcarbonate, potassium bicarbonate, potassium hydroxide, or mixturesthereof. In some embodiments, the alkali metal gasification catalystcomprises one or more potassium complexes formed with coal particulate,carbonates, bicarbonates, hydroxides, or mixtures thereof.

The alkaline earth metal source can be an alkaline earth metal and/or acompound containing alkaline earth metal atoms. Typical alkaline earthmetal sources can include magnesium, calcium, and/or barium sources,such as, but not limited to, magnesium oxide, magnesium hydroxide,magnesium carbonate, magnesium sulfate, calcium oxide, calciumhydroxide, calcium carbonate, calcium sulfate, barium oxide, bariumhydroxide, barium carbonate, barium sulfate, or mixtures thereof. Incertain embodiments, the alkaline earth source comprises a source ofcalcium; in certain other embodiments, the source of calcium is calciumhydroxide, calcium sulfate, or mixtures thereof.

Typically, the quantity of alkaline earth metal source in thecomposition is sufficient to provide from about 0.1 wt % to about 3.0 wt%, or to about 2.0 wt %, alkaline earth atoms by dry weight.

The transition metal gasification catalyst can be a transition metaland/or a compound containing transition metal atoms. Typical transitionmetal gasification catalysts can include sources, such as, but notlimited to, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, or mixtures thereof. Forexample, transition metal gasification catalyst can comprise one or moretransition metal complexes (e.g., coordination complexes formed with oneor more reactive functionalities on the surface or within the pores ofthe coal particulate, such as carboxylic acids and/or phenolic groups).In certain embodiments, the transition metal gasification catalystcomprises an Fe source, Mn source, or mixtures thereof. In certain otherembodiments, the transition metal gasification catalyst comprises one ormore iron or manganese complexes formed with the coal particulate, FeO,Fe₂O₃, FeSO₄, MnO, MnO₂, MnSO₄, or mixtures thereof.

Typically, the quantity of transition metal gasification catalyst in thecomposition is sufficient to provide a ratio of transition metal atomsto carbon atoms ranging from about 0.001 to about 0.10.

Particulate Composition

Typically, the coal source for preparation of the particulatecompositions can be supplied as a fine particulate having an averageparticle size of from about 25 microns, or from about 45 microns, up toabout 500 microns, or up to about 2500 microns. One skilled in the artcan readily determine the appropriate particle size for the individualparticulates and the particulate composition. For example, when a fluidbed gasification reactor is used, the particulate composition can havean average particle size which enables incipient fluidization of theparticulate composition at the gas velocity used in the fluid bedgasification reactor.

The particulate composition can comprise a blend of particulates fromtwo or more sources. The ratio of the coal particulates in theparticulate composition can be selected based on technicalconsiderations, processing economics, availability, and proximity of thecoal sources. The availability and proximity of the sources for theseblends affect the price of the feeds, and thus the overall productioncosts of the catalytic gasification process. For example, an anthracitecoal particulate and a sub-bituminous or lignite coal particulate can beblended in at about 5:95, about 10:90, about 15:85, about 20:80, about25:75, about 30:70, about 35:65, about 40:60, about 45:55, about 50:50,about 55:45, about 60:40, about 65:35, about 70:20, about 75:25, about80:20, about 85:15, about 90:10, or about 95:5 by weight on a wet or drybasis, depending on the processing conditions.

More significantly, the coal sources as well as the ratio the variouscoal particulates can be used to control other materials characteristicsof the feedstock blend. Typically, coal includes significant quantitiesof inorganic mater including calcium, silica, and aluminum, which forminorganic oxides (“ash”) in the gasification reactor. At temperaturesabove about 500° C. to about 600° C., potassium and other alkali metalscan react with ash to form insoluble alkali aluminosilicates. In thisform, the alkali metal is inactive as a catalyst. To prevent buildup ofthe inorganic residue in a gasification reactor, a solid purge of char,i.e., solids composed of ash, unreacted carbonaceous material, andalkali metal bound within the solids, are routinely withdrawn. Catalystloss in the solid purge is generally compensated by a substantialcatalyst make-up stream.

The ash content of the particulate composition can be selected to be,for example, about 20 wt %, 15 wt %, or 10 wt % or lower, depending onratio of the particulates and/or the starting ash in the various coalsources. In other embodiments, the resulting particulate composition cancomprise an ash content ranging from about 5 wt % to about 25 wt %, fromabout 5 wt % to about 20 wt %, from about 10 wt % to about 20 wt %, orfrom about 10 wt % to about 15 wt %, based on the weight of thecomposition. In other embodiments, the ash content of the particulatecomposition can comprise less than about 30 wt %, or less than about 25wt %, or less than about 15 wt %, or less than about 12 wt %, or lessthan about 10 wt %, or less than about 8 wt %, or less than about 6 wt%, alumina, based on the weight of the ash in the particulatecomposition. In certain embodiments, the resulting particulatecomposition can comprise an ash content of less than about 20 wt %,based on the weight of the particulate composition, where the ashcontent of the particulate composition comprises less than about 15 wt %alumina, based on the weight of the ash in the particulate composition.

Such lower alumina values in the particulate composition allow fordecreased losses of alkali catalysts in the gasification process.Typically, alumina can react with alkali source to yield an insolublechar comprising, for example, an alkali aluminate or aluminosilicate.Such insoluble char can lead to decreased catalyst recovery (i.e.,increased catalyst loss), and thus, require additional costs of make-upcatalyst in the overall gasification process, as will be discussedlater.

Additionally, the resulting particulate composition can have asignificantly higher percentage of carbon, and thus btu/lb value andmethane product per unit weight of the particulate composition. Incertain embodiments, the resulting particulate composition has a carboncontent ranging from about 75 wt %, or from about 80 wt %, or from about85 wt %, or from about 90 wt %, up to about 95 wt %, based on thecombined weight of the coal sources.

Methods for Making the Particulate Composition

The coal sources for use in the preparation of the particulatecomposition can require initial processing to prepare the particulatecomposition for gasification. For example, when using a particulatecomposition comprising a mixture of two or more coal sources, eachsource can be separately processed to provide a particulate and addcatalyst thereto, and subsequently mixed. In such a case, one coalsource can be simply crushed into a particulate while the other iscrushed and associated with the various gasification catalyst; the twoparticulates can subsequently be mixed.

The coal sources for the particulate composition can be crushed and/orground separately according to any methods known in the art, such asimpact crushing and wet or dry grinding to yield particulates of each.Depending on the method utilized for crushing and/or grinding of thecoal sources, the resulting particulates may need to be sized (i.e.,separated according to size) to provide an appropriate feedstock.

Any method known to those skilled in the art can be used to size theparticulates. For example, sizing can be performed by screening orpassing the particulates through a screen or number of screens.Screening equipment can include grizzlies, bar screens, and wire meshscreens. Screens can be static or incorporate mechanisms to shake orvibrate the screen. Alternatively, classification can be used toseparate the coal particulate. Classification equipment can include oresorters, gas cyclones, hydrocyclones, rake classifiers, rotatingtrommels, or fluidized classifiers. The coal sources can be also sizedor classified prior to grinding and/or crushing.

Additional feedstock processing steps can be necessary depending on thequalities of the coal sources. High-moisture coals can require dryingprior to crushing. Some caking coals can require partial oxidation tosimplify gasification reactor operation. Coal feedstocks deficient inion-exchange sites can be pre-treated to create additional ion-exchangesites to facilitate catalysts loading and/or association. Suchpre-treatments can be accomplished by any method known to the art thatcreates ion-exchange capable sites and/or enhances the porosity of thecoal feed. See, e.g., previously incorporated U.S. Pat. No. 4,468,231and GB1599932. Often, pre-treatment is accomplished in an oxidativemanner using any oxidant known to the art.

Typically, the coal is wet ground and sized (e.g., to a particle sizedistribution of within the range of about 25 to about 2500 microns) andthen drained of its free water (i.e., dewatered) to a wet cakeconsistency. Examples of suitable methods for the wet grinding, sizing,and dewatering are known to those skilled in the art; for example, seepreviously incorporated U.S. patent application Ser. No. 12/178,380.

The filter cake of the coal particulate formed by the wet grinding inaccordance with one embodiment of the present invention can have amoisture content ranging from about 40% to about 60%, about 40% to about55%, or below about 50%, based on the weight of the filter cake. It willbe appreciated by one of ordinary skill in the art that the moisturecontent of dewatered wet ground coal depends on the particular type ofcoal, the particle size distribution, and the particular dewateringequipment used.

The coal particulate is treated to load the coal particulate with atransition metal gasification catalyst, an alkali metal gasificationcatalyst, and an alkaline earth metal source. The coal particulate istreated in at least three separate processing steps in which separatefeedstocks of coal particulate are contacted with separate solutions.

In some embodiments, a first feedstock is contacted with an aqueoussolution comprising a transition metal gasification catalyst to form aslurry comprising coal particulate and a transition metal gasificationcatalyst; a second feedstock is contacted with an aqueous solutioncomprising an alkaline earth metal source to form a slurry comprisingcoal particulate and an alkaline earth metal source; and a thirdfeedstock is contacted with an aqueous solution comprising an alkalimetal gasification catalyst to form a slurry comprising coal particulateand an alkali metal gasification catalyst. In such embodiments, eachseparate feedstock is contacted with a separate aqueous solution, and nofeedstock is contacted with multiple aqueous solutions. In the slurry,not all of the gasification catalyst or alkaline earth metal source willassociate with the coal particulate. Therefore, when each slurry isdewatered, the recovered aqueous medium will contain gasificationcatalyst or alkaline earth metal source that did not associate with thecoal particulate. Because each feedstock is treated only with a singleaqueous solution, the aqueous medium recovered from the dewateringcontains no (or substantially no) contamination from the aqueoussolutions used to treat the other feedstocks. Therefore, the aqueousmedia recovered from dewatering each sample can be reused to form asubsequent slurry without causing cross-contamination. Also, avoidingcross-contamination can facilitate disposal.

Any methods known to those skilled in the art can be used to associateone or more gasification catalysts and alkaline earth source with thecoal particulate. Such methods include but are not limited to, admixingwith a solid catalyst source and impregnating the catalyst on to coalparticulate. Several impregnation methods known to those skilled in theart can be employed to incorporate the gasification catalysts. Thesemethods include but are not limited to, incipient wetness impregnation,evaporative impregnation, vacuum impregnation, dip impregnation, ionexchanging, and combinations of these methods. Gasification catalystscan be impregnated into the coal particulate by slurrying with asolution (e.g., aqueous) of the catalyst. The solutions for slurryingthe coal particulate can be prepared from fresh transition metalgasification catalyst, alkali metal gasification catalyst, and/oralkaline earth metal source, or may include amounts of transition metalgasification catalyst, alkali metal gasification catalyst, and/oralkaline earth metal source that is recycled from a process of gasifyinga carbonaceous composition into a plurality of gases (described below).

One particular method suitable for combining the coal particulate withthe gasification catalysts and alkaline earth source to provide aparticulate composition where the various components have beenassociated with the coal particulate via ion exchange is described inpreviously incorporated U.S. patent application Ser. No. 12/178,380. Theion exchange loading mechanism is maximized (based on adsorptionisotherms specifically developed for the coal), and the additionalcatalyst retained on wet including those inside the pores is controlledso that the total catalyst target value is obtained in a controlledmanner. Such loading provides a particulate composition as a wet cake.The catalyst loaded and dewatered wet coal cake typically contains, forexample, about 50 wt % moisture. The total amount of catalyst loaded iscontrolled by controlling the concentration of catalyst components inthe solution, as well as the contact time, temperature and method, ascan be readily determined by those of ordinary skill in the relevant artbased on the characteristics of the starting coal.

When the feedstocks of coal particulate are slurried with the solutionsof transition metal gasification catalyst, alkali metal gasificationcatalyst, and alkaline earth metal source, the resulting slurries can bedewatered to provide separate particulate compositions as wet cakes.Methods for dewatering the slurry to provide a wet cake of the catalyzedcoal particulate include filtration (gravity or vacuum), centrifugation,vibratory screening, and/or a fluid press. Typically, when the coalparticulate is treated, via slurrying with an aqueous solution, inseparate steps to provide one or more of the transition metalgasification catalyst, alkali metal catalyst, and alkaline earth source,the slurry is dewatered between each treatment step.

In some embodiments, the dewatered slurries (i.e., wet cakes) of coalparticulate with an aqueous solution of one of the gasificationcatalysts and/or alkaline earth source are thermally treated with a dryinert gas to provide compositions having low residual moisture content.For example, after thermal treatment, the residual moisture content isless than about 6 wt %, or less than about 4 wt %, or less than about 3wt %, or less than about 2 wt %, based on the total weight of thedewatered and thermally treated composition. The thermal treatment may,for example, be carried out in a fluid bed slurry drier, or in anycomparable apparatus known to those of skill in the art.

The at least three separate coal compositions loaded with gasificationcatalyst or an alkaline earth metal source are blended to form aparticulate composition. In some embodiments, at least a part of each ofthe coal compositions (i.e., the coal composition loaded with transitionmetal gasification catalyst, the coal composition loaded with alkalimetal gasification catalyst, and the coal composition loaded withalkaline earth metal source, respectively) is blended to form aparticulate composition.

The combining of the separate loaded coal compositions can occur eitherbefore or after the thermal treatment step. In embodiments where thecombining occurs after thermal treatment, such as described above, thethermally treated compositions are blended according to any methodssuitable for the blending of particulate having low moisture content,including, but not limited to, kneading, and using vertical orhorizontal mixers, for example, single or twin screw, ribbon, or drummixers.

In embodiments where the combining of the dewatered feedstock occursbefore the thermal treatment, at least a portion of each dewatered coalslurry (i.e., the coal composition loaded with transition metalgasification catalyst, the coal composition loaded with alkali metalgasification catalyst, and the coal composition loaded with alkalineearth metal source, respectively) is blended to form a final wet cakeaccording to any methods suitable for the blending of wet cakeparticulate compositions, including, but not limited to, kneading, andusing vertical or horizontal mixers, for example, single or twin screw,ribbon, or drum mixers.

When three or more separate coal compositions (loaded, for example, withtransition metal gasification catalyst, alkali metal gasificationcatalyst, and alkaline earth metal source, respectively) are combined,the separate compositions need not be combined together in a singlestep. In some embodiments, for example, two separate loaded particulatecompositions are combined together (or blended), and then the combinedcompositions are further combined with (or blended) with a third loadedparticulate composition. For example, a coal particulate loaded with atransitional metal gasification catalyst and coal composition loadedwith an alkali metal gasification catalyst are combined, and then thecombined coal particulate composition is combined with a coalcomposition loaded with an alkaline earth metal source. In otherembodiments, a coal particulate loaded with a transitional metalgasification catalyst and coal composition loaded with an alkaline earthmetal source are combined, and then the combined coal particulatecomposition is combined with a coal composition loaded with an alkalimetal gasification catalyst. For example, a coal particulate loaded withan alkaline earth metal source and coal composition loaded with analkali metal gasification catalyst are combined, and then the combinedcoal particulate composition is combined with a coal composition loadedwith a transition metal gasification catalyst.

The particulate composition typically comprises greater than about 50%,or greater than about 70%, or greater than about 85%, or greater thanabout 90%, of the total amount of catalyst loaded onto the coal matrix,for example, as ion-exchanged catalyst on the acidic functional groupsof the coal. The amount of each component associated with the coalparticulate can be determined according to methods known to thoseskilled in the art.

As discussed previously, coal particulates from various sources can becombined appropriately to control, for example, the total catalystloading and/or other qualities of the particulate composition. Theappropriate ratios of the separate particulates will depend on thequalities of the feedstocks as well as the desired properties of theparticulate composition. For example, coal particulates can be combinedin such a ratio to yield a particulate composition having apredetermined ash content, as discussed previously.

In some embodiments, where at least three separate coal feedstocks areused and are loaded with different species (e.g., a first coalcomposition loaded with transition metal gasification catalyst, a secondcoal composition loaded with alkali metal gasification catalyst, and athird coal composition loaded with alkaline earth metal source,respectively), the separate feedstocks may comprise coal compositionsthat are different from each other. For example, in embodimentsemploying three separate feedstocks, each feedstock may comprise a coalcomposition whose ash content and other properties are, for example,more suitable for loading with a particular gasification catalyst and/oralkaline earth metal source. Other factors, including but not limitedto, desired final ash content can also factor into decisions to usecompositionally different coal blends for each of the separatefeedstocks. In other embodiments, however, two or more (or even all) ofthe separate coal feedstocks may have substantially the same composition(e.g., by coal type, ash and mineral content, etc.).

Once dried by thermal treatment, the particulate composition can bestored for future use or transferred to a feed operation forintroduction into a gasification reactor. The particulate compositioncan be conveyed to storage or feed operations according to any methodsknown to those skilled in the art, for example, a screw conveyer orpneumatic transport.

In one particularly useful method, a coal source is wet ground anddewatered to provide a wet cake. The wet cake is associated with agasification catalyst or alkaline earth metal source via slurrying withan aqueous solution of the catalyst or alkaline earth metal source. Thecontacting of the wet cake and the aqueous catalyst solution can occurat temperatures ranging from about 25° C. to about 100° C., or fromabout 25° C. to about 75° C., or from about 50° C. to about 75° C. for apredetermined residence time. After contacting, the slurry is dewatered(e.g., via screening) to yield a wet coal cake loaded with gasificationcatalyst or an alkaline earth metal source. In some embodiments,however, the coal source may be dry ground to form a coal feedstock inparticulate form, and contacted with solution comprising a gasificationcatalyst or alkaline earth metal source as a dry-ground particulate(instead of as a wet cake of coal particulate).

The invention provides carbonaceous compositions that comprise coalparticulate loaded with a transition metal gasification catalyst, coalparticulate loaded with an alkali metal gasification catalyst, and coalparticulate loaded with an alkaline earth metal source. Suchcarbonaceous compositions also include compositions comprisingadditional substances that are suitable for use in a catalyticgasification process. Particularly, such compositions may compriseadditional carbonaceous feedstocks, such as coal, that may or may not beloaded with gasification catalyst or other species that assist in thegasification process. For example, in some embodiments of the invention,the carbonaceous composition additionally comprises a coal particulate(e.g., a low-moisture coal particulate) that is not loaded with anyspecies, such as gasification catalysts, that enhance the gasificationprocess (i.e., an unloaded coal particulate).

When the carbonaceous composition additionally comprises an unloadedcoal particulate, the carbonaceous composition may be prepared by: (1)grinding and sizing the coal particulate (as described above), and (2)blending the unloaded coal particulate with the feedstocks of coalparticulate loaded with gasification catalyst or alkaline earth metalsource.

In some embodiments, a low-moisture coal is dry ground, as describedabove, and is blended with the loaded coal particulate feedstocks whilethe loaded coal particulate feedstocks are in wet cake form (i.e.,before thermal treatment). In embodiments where the separate loaded coalparticulate feedstocks are blended in wet cake form (discussed above),the dry-ground low-moisture unloaded coal particulate may simply beblended with the wet cakes of loaded coal particulate. This can occur ina single step, where the four coal particulate feedstocks (i.e., loadedwith transition metal gasification catalyst (wet cake), loaded withalkali metal gasification catalyst (wet cake), loaded with alkalineearth metal source (wet cake), and unloaded (dry)) are all blendedtogether using any suitable means known to those of skill in the art,including, but not limited to, kneading, and using vertical orhorizontal mixers, for example, single or twin screw, ribbon, or drummixers. The four feedstocks can also be blended in multiple steps. Forexample, two of the loaded coal compositions in wet cake form may beblended together with part of the dry-ground unloaded coal particulatein a first step, and then the third loaded coal composition in wet cakeform and the remainder of the dry-ground unloaded coal particulate canbe added to the mixture in a second step. The number of suitablepermutations for blending the multiple feedstocks in multiple steps isnearly unlimited. In these embodiments, where the dry-ground unloadedcoal particulate is blended with the loaded coal particulates in wetcake form, the resulting blend is thermally treated. Because thedry-ground coal may absorb some of the moisture in the wet cake, thecomposition may dry more readily. Once dried by thermal treatment, theparticulate composition can be stored for future use or transferred to afeed operation for introduction into a gasification reactor.

In some embodiments, a coal particulate is wet ground and dewatered, asdescribed above, and is then blended with the loaded coal particulatefeedstocks while the loaded coal particulate is in wet cake form. Inthese embodiments, both the unloaded coal particulate and the loadedcoal particulate will exist in wet cake form. The various wet cakes canbe blended in a single step or in multiple steps. As mentioned above,the number of suitable permutations for blending the multiple feedstocksin multiple steps is nearly unlimited. After blending, the final wetcake is thermally treated. Once dried by thermal treatment, theparticulate composition can be stored for future use or transferred to afeed operation for introduction into a gasification reactor.

Catalytic Gasification Methods

The particulate compositions of the present invention are particularlyuseful in integrated gasification processes for converting coal tocombustible gases, such as methane.

The gasification reactors for such processes are typically operated atmoderately high pressures and temperature, requiring introduction of theparticulate composition to the reaction zone of the gasification reactorwhile maintaining the required temperature, pressure, and flow rate ofthe feedstock. Those skilled in the art are familiar with feed systemsfor providing feedstocks to high pressure and/or temperatureenvironments, including, star feeders, screw feeders, rotary pistons,and lock-hoppers. It should be understood that the feed system caninclude two or more pressure-balanced elements, such as lock hoppers,which would be used alternately.

In some instances, the particulate composition can be prepared atpressures conditions above the operating pressure of gasificationreactor. Hence, the particulate composition can be directly passed intothe gasification reactor without further pressurization.

Any of several catalytic gasifiers can be utilized. Suitablegasification reactors include counter-current fixed bed, co-currentfixed bed, fluidized bed, entrained flow, and moving bed reactors. Inone embodiment, a fluidized bed gasifier is used.

The particulate compositions are particularly useful for gasification atmoderate temperatures of at least about 450° C., or of at least about600° C. or above, to about 900° C., or to about 750° C., or to about700° C.; and at pressures of at least about 50 psig, or at least about200 psig, or at least about 400 psig, to about 1000 psig, or to about700 psig, or to about 600 psig.

The gas utilized in the gasification reactor for pressurization andreactions of the particulate composition typically comprises steam, andoptionally, oxygen or air, and is supplied to the reactor according tomethods known to those skilled in the art. For example, any of the steamboilers known to those skilled in the art can supply steam to thereactor. Such boilers can be powered, for example, through the use ofany carbonaceous material such as powdered coal, biomass etc., andincluding but not limited to rejected carbonaceous materials from theparticulate composition preparation operation (e.g., fines, supra).Steam can also be supplied from a second gasification reactor coupled toa combustion turbine where the exhaust from the reactor is thermallyexchanged to a water source and produce steam. Alternatively, the steammay be provided to the gasification reactor as described in previouslyincorporated U.S. patent application Ser. No. 12/395,309, entitled“STEAM GENERATION PROCESSES UTILIZING BIOMASS FEEDSTOCKS”, and Ser. No.12/395,320, entitled “REDUCED CARBON FOOTPRINT STEAM GENERATIONPROCESSES”.

Recycled steam from other process operations can also be used forsupplying steam to the reactor. For example, when the slurriedparticulate composition is dried with a fluid bed slurry drier, asdiscussed previously, the steam generated through vaporization can befed to the gasification reactor.

The small amount of required heat input for the catalytic coalgasification reaction can be provided by superheating a gas mixture ofsteam and recycle gas feeding the gasification reactor by any methodknown to one skilled in the art. In one method, compressed recycle gasof CO and H₂ can be mixed with steam and the resulting steam/recycle gasmixture can be further superheated by heat exchange with thegasification reactor effluent followed by superheating in a recycle gasfurnace.

A methane reformer can be included in the process to supplement therecycle CO and H₂ fed to the reactor to ensure that enough recycle gasis supplied to the reactor so that the net heat of reaction is as closeto neutral as possible (only slightly exothermic or endothermic), inother words, that the reaction is run under thermally neutralconditions. In such instances, methane can be supplied for the reformerfrom the methane product, as described below.

Reaction of the particulate composition under the described conditionstypically provides a crude product gas and a char. The char produced inthe gasification reactor during the present processes typically isremoved from the gasification reactor for sampling, purging, and/orcatalyst recovery. Methods for removing char are well known to thoseskilled in the art. One such method taught by EP-A-0102828, for example,can be employed. The char can be periodically withdrawn from thegasification reactor through a lock hopper system, although othermethods are known to those skilled in the art. Processes have beendeveloped to recover alkali metal from the solid purge in order toreduce raw material costs and to minimize environmental impact of a CCGprocess.

The char can be quenched with recycle gas and water and directed to acatalyst recycling operation for extraction and reuse of the alkalimetal catalyst. Particularly useful recovery and recycling processes aredescribed in U.S. Pat. No. 4,459,138, as well as previously incorporatedU.S. Pat. No. 4,057,512 and US2007/0277437A1, and previouslyincorporated U.S. patent application Ser. Nos. 12/342,554, 12/342,715,12/342,736 and 12/343,143. Reference can be had to those documents forfurther process details.

Crude product gas effluent leaving the gasification reactor can passthrough a portion of the gasification reactor which serves as adisengagement zone where particles too heavy to be entrained by the gasleaving the gasification reactor (i.e., fines) are returned to thefluidized bed. The disengagement zone can include one or more internalcyclone separators or similar devices for removing fines andparticulates from the gas. The gas effluent passing through thedisengagement zone and leaving the gasification reactor generallycontains CH₄, CO₂, H₂ and CO, H₂S, NH₃, unreacted steam, entrainedfines, and other contaminants such as COS.

The gas stream from which the fines have been removed can then be passedthrough a heat exchanger to cool the gas and the recovered heat can beused to preheat recycle gas and generate high pressure steam. Residualentrained fines can also be removed by any suitable means such asexternal cyclone separators, optionally followed by Venturi scrubbers.The recovered fines can be processed to recover alkali metal catalyst,or directly recycled back to feedstock preparation as described inpreviously incorporated U.S. patent application Ser. No. 12/395,385,entitled “CARBONACEOUS FINES RECYCLE”.

The gas stream from which the fines have been removed can be fed to COShydrolysis reactors for COS removal (sour process) and further cooled ina heat exchanger to recover residual heat prior to entering waterscrubbers for ammonia recovery, yielding a scrubbed gas comprising atleast H₂S, CO₂, CO, H₂, and CH₄. Methods for COS hydrolysis are known tothose skilled in the art, for example, see U.S. Pat. No. 4,100,256.

The residual heat from the scrubbed gas can be used to generate lowpressure steam. Scrubber water and sour process condensate can beprocessed to strip and recover H₂S, CO₂ and NH₃; such processes are wellknown to those skilled in the art. NH₃ can typically be recovered as anaqueous solution (e.g., 20 wt %).

A subsequent acid gas removal process can be used to remove H₂S and CO₂from the scrubbed gas stream by a physical absorption method involvingsolvent treatment of the gas to give a cleaned gas stream. Suchprocesses involve contacting the scrubbed gas with a solvent such asmonoethanolamine, diethanolamine, methyldiethanolamine,diisopropylamine, diglycolamine, a solution of sodium salts of aminoacids, methanol, hot potassium carbonate or the like. One method caninvolve the use of SELEXOL® (UOP LLC, Des Plaines, Ill. USA) orRECTISOL® (Lurgi A G, Frankfurt am Main, Germany) solvent having twotrains; each train consisting of an H₂S absorber and a CO₂ absorber. Thespent solvent containing H₂S, CO₂ and other contaminants can beregenerated by any method known to those skilled in the art, includingcontacting the spent solvent with steam or other stripping gas to removethe contaminants or by passing the spent solvent through strippercolumns. Recovered acid gases can be sent for sulfur recoveryprocessing. The resulting cleaned gas stream contains mostly CH₄, H₂,and CO and, typically, small amounts of CO₂ and H₂O. Any recovered H₂Sfrom the acid gas removal and sour water stripping can be converted toelemental sulfur by any method known to those skilled in the art,including the Claus process. Sulfur can be recovered as a molten liquid.Stripped water can be directed for recycled use in preparation of thecatalyzed feedstock. One method for removing acid gases from thescrubbed gas stream is described in previously incorporated U.S. patentapplication Ser. No. 12/395,344, entitled “SELECTIVE REMOVAL ANDRECOVERY OF ACID GASES FROM GASIFICATION PRODUCTS”.

The cleaned gas stream can be further processed to separate and recoverCH₄ by any suitable gas separation method known to those skilled in theart including, but not limited to, cryogenic distillation and the use ofmolecular sieves or ceramic membranes, or via the generation of methanehydrate as disclosed in previously incorporated U.S. patent applicationSer. No. 12/395,330, entitled “PROCESS AND APPARATUS FOR THE SEPARATIONOF METHANE FROM A GAS STREAM”. Typically, two gas streams can beproduced by the gas separation process, a methane product stream and asyngas stream (H₂ and CO). The syngas stream can be compressed andrecycled to the gasification reactor. If necessary, a portion of themethane product can be directed to a reformer, as discussed previouslyand/or a portion of the methane product can be used as plant fuel.

1. A process for preparing a particulate composition, the process comprising the steps of: (a) providing a first coal feedstock, a second coal feedstock, and a third coal feedstock, each in particulate form; (b) contacting the first coal feedstock with a first aqueous solution comprising a transition metal gasification catalyst to form a first slurry; (c) contacting the second coal feedstock with a second aqueous solution comprising alkaline earth metal source to form a second slurry; (d) contacting the third coal feedstock with a third aqueous solution comprising an alkali metal gasification catalyst to form a third slurry; and (e) dewatering the first slurry, the second slurry, and the third slurry to form a first wet cake, a second wet cake, and a third wet cake, respectively; wherein the process comprises the further steps of (1) or (2): (1) (f1) thermally treating the first wet cake, the second wet cake, and the third wet cake with a dry inert gas to provide a first particulate, a second particulate, and a third particulate, each having a residual moisture content of less than about 4 wt %; and (g1) blending at least a portion of the first particulate, at least a portion of the second particulate, and at least a portion of the third particulate to form a particulate composition; or (2) (f2) combining at least a portion of the first wet cake, at least a portion of the second wet cake, and at least a portion of the third wet cake to form a final wet cake; (g2) thermally treating the final wet cake with a dry inert gas to provide a particulate composition having a residual moisture content of less than about 4 wt %.
 2. The process according to claim 1, wherein the process comprises the further steps of (1).
 3. The process according to claim 1, wherein the process comprises the further steps of (2).
 4. The process according to claim 3 further comprising: providing a fourth coal feedstock in particulate form that comprises a dry-ground low-moisture coal; and combining the fourth coal feedstock in particulate form with the first wet cake, the second wet cake, and the third wet cake in step (f2) to form a final wet cake.
 5. The process according to claim 1, wherein the alkali metal gasification catalyst comprises a source of potassium and/or sodium.
 6. The process according to claim 1, wherein the alkaline earth metal source comprises a source of calcium, magnesium and/or barium.
 7. The process according to claim 1, wherein the transition metal gasification catalyst comprises Fe, Mn, or mixtures thereof.
 8. The process according to claim 1, wherein the alkali metal gasification catalyst comprises a source of potassium and/or sodium; the alkaline earth metal source comprises a source of calcium, magnesium and/or barium; and the transition metal gasification catalyst comprises Fe, Mn or mixtures thereof. 